Platelet-derived growth factor BB induces nuclear export and proteasomal degradation of CREB via phosphatidylinositol 3-kinase/Akt signaling in pulmonary artery smooth muscle cells.

Abstract

Cyclic AMP response element binding protein (CREB) content is diminished in smooth muscle cells (SMCs) in remodeled pulmonary arteries from animals with pulmonary hypertension and in the SMC layers of atherogenic systemic arteries and cardiomyocytes from hypertensive individuals. Loss of CREB can be induced in cultured SMCs by chronic exposure to hypoxia or platelet-derived growth factor BB (PDGF-BB). Here we investigated the signaling pathways and mechanisms by which PDGF elicits depletion of SMC CREB. Chronic PDGF treatment increased CREB ubiquitination in SMCs, while treatment of SMCs with the proteasome inhibitor lactacystin prevented decreases in CREB content. The nuclear export inhibitor leptomycin B also prevented depletion of SMC CREB alone or in combination with lactacystin. Subsequent studies showed that PDGF activated extracellular signal-regulated kinase, Jun N-terminal protein kinase, and phosphatidylinositol 3 (PI3)-kinase pathways in SMCs. Inhibition of these pathways blocked SMC proliferation in response to PDGF, but only inhibition of PI3-kinase or its effector, Akt, blocked PDGF-induced CREB loss. Finally, chimeric proteins containing enhanced cyan fluorescent protein linked to wild-type CREB or CREB molecules with mutations in several recognized phosphorylation sites were introduced into SMCs. PDGF treatment reduced the levels of each of these chimeric proteins except for one containing mutations in adjacent serine residues (serines 103 and 107), suggesting that CREB loss was dependent on CREB phosphorylation at these sites. We conclude that PDGF stimulates nuclear export and proteasomal degradation of CREB in SMCs via PI3-kinase/Akt signaling. These results indicate that in addition to direct phosphorylation, proteolysis and intracellular localization are key mechanisms regulating CREB content and activity in SMCs.

• Authors: Chrystelle V Garat, Dana Fankell, Paul F Erickson, Jane E-B Reusch, Natalie N Bauer, Ivan F McMurtry, Dwight J Klemm
• Journal: Molecular and cellular biology (Mol Cell Biol) Vol. 26 Issue 13 Pg. 4934-48 (Jul 2006) ISSN: 0270-7306 [Print] United States
• PMID: 16782881 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• Cyclic AMP Response Element-Binding Protein
• Cysteine Proteinase Inhibitors
• Fatty Acids, Unsaturated
• Phosphoinositide-3 Kinase Inhibitors
• Platelet-Derived Growth Factor
• Proteasome Inhibitors
• Proto-Oncogene Proteins c-sis
• Recombinant Fusion Proteins
• Ubiquitin
• lactacystin
• Becaplermin
• Serine
• Proto-Oncogene Proteins c-akt
• Proteasome Endopeptidase Complex
• Acetylcysteine
• leptomycin B

Topics

• Acetylcysteine (analogs & derivatives, pharmacology)
• Active Transport, Cell Nucleus (drug effects)
• Animals
• Becaplermin
• Cell Proliferation (drug effects)
• Cyclic AMP Response Element-Binding Protein (analysis, genetics, metabolism)
• Cysteine Proteinase Inhibitors (pharmacology)
• Fatty Acids, Unsaturated (pharmacology)
• Humans
• Mutation
• Myocytes, Smooth Muscle (chemistry, drug effects, enzymology)
• Phosphatidylinositol 3-Kinases (metabolism)
• Phosphoinositide-3 Kinase Inhibitors
• Phosphorylation
• Platelet-Derived Growth Factor (pharmacology)
• Proteasome Endopeptidase Complex (metabolism)
• Proteasome Inhibitors
• Proto-Oncogene Proteins c-akt (antagonists & inhibitors, metabolism)
• Proto-Oncogene Proteins c-sis
• Pulmonary Artery (cytology, drug effects, enzymology)
• Rats
• Recombinant Fusion Proteins (analysis, genetics)
• Serine (genetics, metabolism)
• Signal Transduction
• Ubiquitin (metabolism)